Clara Cell “10 kDa” protein (CC10) or uteroglobin (UG) is a small, homodimeric secretory protein produced by several mucosal epithelia and other organs of epithelial origin (Mukherjee, 1999). CC10 consists of two identical subunits of 70 amino acid residues, each with the “four helical bundle” secondary structure motif, joined in antiparallel orientation by two disulfide bonds between Cys 3 and 69′, 3′ and 69 (Matthews, 1994;
Morize, 1997). CC10 is the first member of an emerging family of small globular proteins that share the same secondary, tertiary and quaternary structure and are thought to mediate similar functions. The homodimer containing two disulfide bonds appears to be its primary form. In humans, the lung is the main site of CC10 production, while several other organs synthesize smaller amounts of mRNA encoding this protein (Singh, 1987; Sandmoller, 1994). CC10 is an anti-inflammatory and immunomodulatory protein that has been characterized with respect to various interactions with other proteins, receptors and cell types (reviewed in Mukherjee, 1999 and Pilon, 2000). Lower levels of CC10 protein or mRNA have been found in various tissue and fluid samples for a number of clinical conditions characterized by some degree of inflammation including pneumonia (Nomori, 1995).
The physiology of CC10 protein in different types of pulmonary infections has been studied in one strain of CC10 knockout mouse. In two studies in which CC10 knockout and wild type mice were each infected with either Pseudomonas aeruginosa or adenovirus, two common human respiratory pathogens, the wild type mice experienced more rapid clearing of the pathogens, with greater killing of the pathogens by the innate immune system, suggesting a benefit to CC10 deficiency during viral and bacterial infection (Hayashida, 1999; Harrod, 1998). This is consistent with earlier observations in which CC10 was reported to be an immunosuppressive agent (Dierynck, 1995; 1996), indicating that CC10 would suppress the natural immune response to an infection, whether bacterial or viral, including influenza. Thus, the administration of CC10 in the presence of a viral or bacterial respiratory infection could not be expected to benefit the patient. Subsequently, it was reported that restoration of CC10 function using recombinant human CC10 protein (rhCC10) prior to infection with respiratory syncytial virus (RSV), enabled a more rapid clearance of the infection than in untreated knockout mice (Wang, 2003). However, a recent study showed that rhCC10 can prevent the development of acquired immunity, specifically antigen-specific T cells, when present at the same time that dendritic cells are exposed to antigen (Johansson, 2007), which again indicates that administration of rhCC10 may not benefit a patient with an infection. Thus, the current state of knowledge regarding the potential hazards or benefits of rhCC10 treatment during a respiratory infection is conflicting and allows no conclusions to be drawn regarding the safe and/or efficacious use of CC10 to treat different types of respiratory infections. No information regarding the effect of CC10 on influenza infection is available. We report herein, direct verification of the efficacy of rhCClO against influenza Type A in vivo, direct verification of the anti-viral effects of CC10 at the cellular level, its mechanism of action, and its potential use to treat and/or prevent viral infection, and, in particular, influenza infection.
Influenza has caused four major outbreaks (1889, 1918, 1957, and 1968) in the past 120 years, causing the deaths of an estimated 50-100 million people worldwide. Influenza is an orthomyxovirus, an RNA virus that is transmitted by aerosols as well as by direct contact of contaminated surfaces with nasal mucosa and targets respiratory epithelial cells. Influenza infection may cause severe symptoms, including fever, sore throat and muscle aches, malaise, weight loss, respiratory congestion, and sometimes respiratory failure and death. Influenza elicits an acquired immune response (cytotoxic T cells and antibodies) that typically clears the infection in 1-2 weeks in normal healthy individuals. Several subtypes of influenza that infect humans, including avian influenza (H5N1), seasonal influenza H3N2, and swine flu (H1N1), can be treated with antiviral agents such as neuraminidase inhibitors. However, the rapid rate of mutation in influenza has led to the development of drug-resistant strains (Moscona, 2009), such that widespread use of antiviral agents for prevention and or treatment will lead to acceleration of the development of resistance to these drugs. New therapeutic agents are therefore needed to treat, cure and prevent influenza infection. Likewise, there are no approved therapies for the vast majority of viral infections in the respiratory tract and other body systems.